1. Field of the Invention
The present invention relates to a camera having a zoom lens, and more particularly, relates to a camera having a zoom lens which can use both a photosensitive film and an image pick-up device such as a CCD for taking pictures.
2. Description of the Related Art
In recent years, a still camera using both a photosensitive film (e.g., silver-halide film) and an image pick-up device (e.g., a CCD) for taking pictures has been proposed. In this type of camera, an object image is focused on either the photosensitive film or the image pick-up device when the object image is photographed. When the object image is photographed using the image pick-up device, the object image is recorded in the form of image signals. If such type of camera is provided with a zoom lens, a state of zooming of the zoom lens can be viewed through the viewfinder if the camera is an SLR (single-lens-reflex) camera; i.e., the magnification of the viewfinder changes synchronously with the variation of the focal length of the zoom lens. However, in a camera in which the optical viewfinder is provided independently of the zoom lens, in order to make the magnification of the viewfinder change synchronously with the variation of the focal length of the zoom lens, it is necessary to provide the camera with a viewfinder zoom mechanism for the optical viewfinder in addition to the photographic lens zoom mechanism, wherein these two zoom mechanisms need to be driven in association with each other when the zooming operation is carried out.
Accordingly, in the camera in which the optical viewfinder is provided independently of the zoom lens and uses both a photosensitive film and an image pick-up device, both the optical viewfinder zoom mechanism and the photographic lens zoom mechanism are driven when the zooming operation is carried out. When the zooming operation is carried out, the photographic lens zoom mechanism consumes much electric power because (in general) at least one lens group having a relatively large diameter in the zoom lens needs to be driven. Power consumption is therefore high, which cannot be ignored. In a photographic operation with such a camera, the focal length is generally changed repeatedly to obtain a desired focal length while changing the angle of view before a shutter is released. Such an operation requires both the optical viewfinder zoom mechanism and the photographic lens zoom mechanism to also be driven repeatedly, consuming a considerable amount of electric power, shortening the battery life span. In order to overcome this problem, a camera having a zoom lens and a fixed-focus optical viewfinder has been proposed. This camera consumes less power because it is not necessary to provide the camera with any drive mechanism for electrically driving the optical viewfinder. However, this type of camera still consumes a considerable amount of battery power, as the photographic lens zoom mechanism is repeatedly driven before a shutter release.
The primary object of the present invention is to provide a camera having a zoom lens wherein power consumption for the zooming operation of the camera is reduced by limiting the zooming operation of the zoom lens and/or the optical viewfinder of the camera.
To achieve the object mentioned above, according to an aspect of the present invention, there is provided a camera including: a zoom lens, having a first zoom mechanism, for photographing an image of an object; a focal length setting device which controls the zoom mechanism to set a focal length of the zoom lens; and a electronic monitoring device for visually displaying the object image; wherein the electronic monitoring device displays the object image which corresponds to the focal length set by the focal length setting device at all times; and the focal length setting device actuates the zoom mechanism to set the focal length of the zoom lens at a set focal length only at the time immediately before a photographing operation is carried out.
Preferably, the camera is also provided with: an optical viewfinder provided independently of the zoom lens; an image pick-up device positioned in either an optical system of the zoom lens or an optical system of the viewfinder; and a signal processing circuit for processing image signals output from the image pick-up device to display the image signals as an image on the electronic monitoring device. The signal processing circuit includes an electronic zoom circuit for performing an electronic zoom process in which only a portion of image signals obtained from the image pick-up device are processed to display an enlarged image corresponding to the portion of image signals on the electronic monitoring device, the portion of image signals corresponding to the focal length set by the focal length setting device.
Preferably, the camera is also provided with: a second zoom mechanism for moving at least one optical element of the optical viewfinder; wherein the first zoom mechanism is for moving at least one optical element of the zoom lens; the first zoom mechanism engages with the second zoom mechanism so that a focal length of the optical viewfinder varies according to the variation of the focal length of the zoom lens, and the image pick-up device is positioned in the optical viewfinder.
Preferably, the camera is also provided with: a distance measuring device for measuring an object distance of the object to obtain distance data; a distance-data detector for repeatedly detecting the distance data; and an actuating device for actuating the first zoom mechanism, so that the focal length setting device actuates the zoom mechanism to set the zoom lens at the set focal length immediately after the number of detections of the distance-data detector reaches a predetermined number when a value of the distance data is within a predetermined value.
Preferably, the distance-data detector repeatedly detects the distance data at predetermined intervals when a release button of the camera is half depressed.
Preferably, the focal length setting device actuates the first zoom mechanism to set the zoom lens at the set focal length when the set focal length is smaller than a current focal length of the zoom lens.
Preferably, the focal length setting device does not actuate the first zoom mechanism when the set focal length is equal to or greater than the current focal length of the zoom lens.
Preferably, the focal length setting device actuates the first zoom mechanism to set the focal length of the zoom lens to the set focal length only at a time immediately before a shutter release.
Preferably, the camera includes an optical viewfinder provided independently of the zoom lens.
Preferably, the camera is an SLR camera.
Preferably, the electronic monitoring device is an LCD monitor.
According to another aspect of the present invention, there is provided a camera including: an optical zoom lens system; an optical zoom viewfinder system; a first zoom mechanism for moving at least one optical element of the optical zoom lens system to change the focal length thereof; a second zoom mechanism for moving at least one optical element of the optical zoom viewfinder system to change the focal length thereof, the second zoom mechanism system engaging with the first zoom mechanism system so that a focal length of the optical zoom viewfinder system varies synchronously with variation of a focal length of the optical zoom lens system; an image pick-up device positioned in either the optical zoom lens system or the optical zoom viewfinder system; an electronic monitor for visually displaying an object image obtained through the image pick-up device; an electronic zoom device for performing an electronic zoom process in which a portion of the object image, obtained through the image pick-up device, is enlarged to be displayed on the electronic monitor; and a focal length setting device which controls the first zoom mechanism to set a focal length of the optical zoom lens system; wherein the electronic monitor displays the object image at the focal length set by the focal length setting device at all times, and wherein the focal length setting device actuates the first zoom mechanism to set the optical zoom lens system to the set focal length only at the time immediately before a shutter release.
According to the present invention, since the object image is displayed at the focal length set by the focal length setting device on the electronic monitoring device at all times before taking a picture, the angle of view of the object can be checked by the user of the camera at all times even if the zoom mechanism for driving the zoom lens is not driven. At the time of taking a picture, the focal length of the zoom lens is set at a set focal length by the focal length setting device so that a picture may be taken through the zoom lens. Accordingly, either the zoom mechanism of the zoom lens or the zoom mechanism of the optical viewfinder need not be driven until the moment immediately before the object is photographed, so that the power consumption for the zoom mechanism of the camera can be reduced, extending the life time of battery.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-221237 (filed on Aug. 5, 1998) which is expressly incorporated herein by reference in its entirety.